Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
It is known that the control of computers or computer activated devices can be achieved by monitoring human eye movements, including eye gaze direction. Eye gaze tracking systems normally require a calibration step to accurately determine the subject's line of sight (calibrated gaze direction) and/or the subject's point of regard (intersection of the calibrated gaze direction with a specific area). This is because each subject will possess a different ocular profile. Generally, the calibration step requires the subject to fixate on one or more known points (typically locations on a screen) whilst gaze direction measurements are recorded. The set of gaze direction measurements are then used to calibrate the gaze direction algorithm to improve overall accuracy.
The calibration process takes time and requires learning and cooperation from the user, which places a limitation on the suitability of current gaze tracking systems for many applications. Furthermore, periodic re-calibration due to environmental changes or eye fatigue can be required.
Within the prior art, various schemes exist aimed at improving on the eye gaze calibration process, including:
Witt et al. (U.S. Pat. No. 6,873,714) discloses an eye tracking system that creates an ocular profile for each new user through standard calibration methods. The subject's unique ocular profile is stored for later retrieval based on identification of the user via facial feature recognition. In this way calibration need only be performed once per user however user concentration and cooperation is still required for the initial calibration.
Pilu (U.S. Patent Application 2005/0225723) discloses an eye tracking system that is calibrated by comparing a user's measured eye gaze measurement statistics with a pre-measured set of eye gaze measurement statistics to determine a calibration correction factor that is calculated to give an optimum match between the two measurement sets. Disadvantageously, comparison to a pre-measured set of statistics is required for calibration.
Vertegaal et al. (U.S. Patent Application 2005/0175218) discloses an eye tracking system that is calibrated by using eye reflections (glints) caused by a plurality of illuminator markers at known locations. Disadvantageously, uniquely identifiable hardware markers are required for calibration.
There is still a desire in the art to make the calibration process simpler, unobtrusive, and not reliant on the cooperation of the subject.